The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE®) suggests a ventilation and acceptable indoor air quality in low-rise residential buildings standard in ASHRAE® Standard 62.2. ASHRAE® Standard 62.2 is hereby incorporated by reference as providing informational background to the present invention.
Standard 62.2 establishes a number of minimum ventilation standards for residential buildings, with various standards suggested over relatively short to relatively long time periods (i.e. from one to twenty four hour periods). These standards call for fresh air to be ventilated into a house or other low rise residential building to at least a minimum level.
FIG. 1 shows a schematic view of a building 20 that includes an HVAC system shown generally at 10. The illustrative HVAC system includes a heating device 12, a cooling device 14, a heat exchanger 16, and a fan 18. Ductwork connects the system 10 to various rooms in the building 20. A controller 22 receives indoor environment information from one or more sensors 24 (which may be, for example, a thermostat or humidistat), and controls various elements of the system 10.
The illustrative HVAC system 10 also includes a fresh air vent 26 that is coupled to the system 10 via a selectively openable damper 28. The inclusion of the fresh air vent 26 and selectively openable damper 28 allows for a controllable infusion of fresh air into the interior of the building 20. For air to enter, the damper 28 can be opened and the fan 18 can be operated, so that fresh air is sucked into the building 20 by the action of the fan 18.
The addition of fresh air to the interior of the building 20 can be used to meet a desired threshold of fresh air ventilation, such as that suggested in Standard 62.2. However, over ventilation of the building 20 can be undesirable in some cases because it can increase the cost of operating the building 20. For example, operating the fan 18 for the sole purpose of drawing fresh air into the building 20 can increase the power consumed by the fan 18, and thus increase the cost of operating the building 20. Also, the fresh air that is drawn into the building 20 may be at a different temperature and/or humidity than that which is desired, and thus may require additional conditioning (i.e. heating, cooling, drying, humidifying, etc.), which can increase the cost of operating the HVAC system. Because the desired ventilation strategy for different buildings can vary considerably depending on the circumstances, it may be desirable to provide added flexibility to a user or installer to choose an appropriate ventilation control strategy.